Fix the panel configuration width in case of long strings in buttons.
Review Request #123815 - Created May 16, 2015 and submitted
The panel configuration width is defined to a fixed value when it's vertical.
In English, it's not a problem because strings are very compacts. But for example, in French, some strings get too big for the buttons.
The width is now computed dynamically from the button layout.
I'm really not a QML expert, please let me know if there is a better way to achieve that.
Tested in all screen edges.